Need help on choosing electric fuel pump for carbed 5.9

RustyRatRod said
I like the old school Carter 4601HP. You'll need a regulator and a return ain't a bad idea.

I was planning on doing a return style regulator and a line back to the tank. Going to run new 3/8" hard line.
Can I use the original 5/16" line for the return? Or do i need to go 3/8" with that too?